This invention relates to a battery powered device, and more particularly to an apparatus and method for predicting and indicating the number of remaining hours that the device can be operated until the battery must be replaced or recharged.
In many applications where portable battery powered devices are used, it is desirable to have an advance indication of the amount of remaining battery life in the device so that the user will know how much longer he can use the device before it is necessary to stop and either replace or recharge the batteries. Several prior patents, such as U.S. Pat. Nos. 3,118,137; 4,525,055; and 4,553,081, for example, disclose battery powered devices which are equipped with circuits or methods to indicate remaining battery life. However, the devices described in these patents employ somewhat complicated and specialized means for providing an indication of remaining battery life, which would be inconvenient or undesirably expensive to implement in many applications. Moreover, many of the prior approaches to providing an indication of remaining battery life do not take into account the fact that the expected useful life of a rechargeable battery changes during its lifetime after repeated discharge-recharge cycles.
With the foregoing in mind, it is an object of the present invention to provide a simple, inexpensive and easily implemented apparatus and method for predicting the remaining useful life of the battery in a battery powered device.
A further object of the present invention is to provide an apparatus and method of the type described which takes into account the deterioration of the useful battery life over the lifetime of the battery.
A further object of the invention is to provide a battery life prediction apparatus and method of the type described which makes use of a microprocessor already provided in the device itself so as to minimize the need for additional parts.